398 Defeription of a Ventilator 
the underfide af the deck = 5 tons = to the quantity of mé« 
phitic air confined ; fuch being the lighteft fluid, the major 
part of it would, ie after the commencement of the ope- 
ration, be Seen, by the atmofpheric air, to vent itfelf at the 
holes previded for that purpofe; and the remainder of the 
hour being employed in the like ventilation, five tons of freth 
air would pafs above twenty: times repeatedly amidft the 
grains, to cool, refrefh, and fweeten the cargo. A purifica- 
tion thus adminiftered once in eight-and-forty hours, would, 
I conceive, be amply fufficient to preferve the corn from taint 
or injury, be the voyage ever fo tedious ; and unlefs it fhould 
by neglect. have overheated and grown together, or fettled 
- teo clofe, the labour would be that of a boy only; for the 
dairy-girl at her churn works harder than he otherwife need 
to do at this. 
My air-veflel is, for the fake of cheapnefs, confined to the 
narrow diameter of ten-inches ; but, as the contents of circles 
are proportionate to the fquare of their diameters, by enlarg- 
ing that, you increafe their power accordingly ; wherefore, 
fy extending the diameter to fourteen inches, the contents 
will be nearly doubled; and, by adding ten inches more ‘to 
the Jength of the ftroke, you almott treble the difcharge of 
No. 1, and obtain a power capable of ventilating a cargo of 
400 tons within the hour. But the air-veffel muft be length- 
ened; the pipes at the fame time enlarged; the metal of 
which the whole is conftructed be in fub{tance proportion- 
able; and the labour be that of a man, or perhaps two upon 
occafion. 
A ventilator, on the plan and dimenfions here propofed, 
would come within the compafs, I fhould think, of five or 
fix guineas. One on the larger feale, caufed by the increafed 
fubftance of the metal, and the extra fize and length of the 
pipes, might amount to twenty; which, in either, 1s under 
fourpence per quarter on the firft cago; and as they will 
laft many years if well painted, and, when not in ufe, taken 
to pieces and put carefully by, I flatter myfelf it is an expe- 
riment well worth trial; particularly if a premium be offered 
to the fhip-owner, who, by means of fuch machine, imports 
his corn pure and untainted from a diflant land. 
Objeions 
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